The English translation of the Bhikkhu-vibhanga: the first part of the Suttavibhanga, which itself is the first book of the Pali Vinaya Pitaka, one of the three major ‘baskets’ of Therevada canonical literature. It is a collection of rules for Buddhist monks.
The English translation of the Vinaya-pitaka (first part, bhikkhu-vibhanga) contains many...

“Just as we amuse ourselves in a boat with our wives, so do these recluses, sons of the Sakyans, having arranged together with nuns, amuse themselves in a boat.”

Monks heard these people who … spread it about. Those who were modest monks … spread it about, saying:

“How can this group of six monks, having arranged together with nuns, embark in one boat?” …

“Is it true, as is said, that you, monks, having arranged together with nuns, embarked in one boat?”

“It is true, lord.”

The enlightened one, the lord, rebuked them, saying:

“How can you, foolish men … embark in one boat? It is not, foolish men … And thus, monks, this rule of training should be set forth:

“Whatever monk, having arranged together with a nun, should embark in one boat, going either upstream or downstream, there is an offence of expiation.”

And thus this rule of training for monks came to be laid down by the lord. Vin.4.65

Bu-Pc.28.2.1 Now[1] at that time several monks and nuns were going along the high-road from Sāketa to Sāvatthī. On the way there was a river to be crossed. Then these nuns spoke thus to these monks:

“We will cross over together with the masters.”

BD.2.293 “Sisters, it is not allowable, having arranged together with a nun, to embark in one boat. Either you cross over first, or we will cross over (first).”

“Honoured sirs, the masters are the highest men, so let the masters cross over first.”

Then as those nuns were crossing over last thieves robbed them and assaulted them. Then these nuns, having arrived at Sāvatthī, told this matter to the nuns. The nuns … to the monks. The monks … to the lord. Then the lord on this occasion, in this connection, having given reasoned talk, addressed the monks, saying:

“I allow you, monks, to embark in one boat, having arranged together with a nun, if it is for crossing over to the other bank. And thus, monks, this rule of training should be set forth:

“Whatever monk, having arranged together with a nun, should embark in one boat, going either upstream or downstream, except for crossing over to the other bank, there is an offence of expiation.”

Having arranged[2] means: if one arranges, saying, ‘We are embarking, sister, we are embarking, master, we are embarking, master, we are embarking, sister, we are embarking either today or tomorrow or the next day,’ there is an offence of wrong-doing. If the monk embarks when the nun has embarked, there is an offence of expiation. If the nun embarks when the monk has embarked, there is an offence of expiation. Or if both embark there is an offence of expiation.

Except for crossing over to the other bank means: setting aside for crossing over to the other bank.

In a village close enough for a cock (to walk), among every (such) village, there is an offence of expiation. For every half yojana in what is not a village, in a jungle, there is an offence of expiation.[7]

Bu-Pc.28.3.2 If he thinks that it was arranged when it was arranged (and) embarks in the same boat, going either upstream or downstream, except for crossing over to the other bank, Vin.4.66 there is an offence of expiation. If he is in doubt as to whether it was arranged … see Bu-Pc.27.3.2 … no offence.

Bu-Pc.28.3.3 There is no offence if it is for crossing over to the other bank[8]; if they embark not having arranged; if the nun arranges (and) the monk does not arrange; if they embark without (making) a rendezvous; if there are dangers; if he is mad, if he is the first wrong-doer.[9]

Vin-a.809 says, ‘here it is not only the river, for there is no offence for one who goes from the port of a great ford to Tāmalitti or Suvaṇṇabhūmi.’ Tāmalitti was a sea-port (the modern Tamluk), formerly on the estuary of the Ganges, and the port from where Asoka sent the branch of the Bodhi-tree to Ceylon.
Suvaṇṇabhūmi is the modern Cambodia (Pali-English Dictionary); or more probably Lower Burma (Pegu and Moulmein districts), according to B.C. Law, Geography of Early Buddhism, p.70, the Pagan and Moulmein districts, according to Dictionary of Pali Proper Names; mentioned at Mnd.155, Sāsanavaṃsa 10, where it is said that it stands near the great sea.